@misc{cryptoeprint:2000:052,
author = {Slobodan Petrovic and Amparo Fúster-Sabater},
title = {CRYPTANALYSIS OF THE A5/2 ALGORITHM},
howpublished = {Cryptology ePrint Archive, Report 2000/052},
year = {2000},
note = {\url{http://eprint.iacr.org/}},
}
You will need the url.sty package (comes with most LaTeX installations) for the last line. Otherwise, remove the \url command.